Greedy Mouse

Greedy Mouse

时间限制： 1000 ms  |  内存限制： 65535 KB

难度： 3

描述

A fat mouse prepared M pounds of cat food,ready to trade with the cats guarding the warehouse containing his

favorite food:peanut. The warehouse has N rooms.The ith room containsW[i] pounds of peanut and requires 

F[i] pounds of cat food. Fatmouse does not have to trade for all the peanut in the room,instead,he may get 

 W[i]*a% pounds of peanut if he pays F[i]*a% pounds of cat food.The mouse is a stupid mouse,so can you tell 

him the maximum amount of peanut he can obtain.

输入

The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers W[i] and F[i] respectively. The test case is terminated by two -1. All integers are not greater than 1000.

输出

For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of penaut that FatMouse can obtain.

样例输入

5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1

样例输出

13.333
31.500

#include<stdio.h>
#include<stdlib.h>


typedef struct
{
  double w;
  double f;        
}waho;


waho s[10001];


int comp ( const void *a, const void *b )  
{  
     return  ((*( waho * )a).w / (*(waho *)a).f ) >   
            ((*( waho * )b).w/  (*(waho *)b).f )   ? -1:1 ;  
}


void mxpea(waho wh[],int n,double m)            //贪心选择 w/f最大者    
{  
    int i;  
    double res=0;  
    double tem;  
    for (i=0;i<n;i++)  
    {  
        if (m>wh[i].f)   
        {  
            res+=wh[i].w;  
            m-=wh[i].f;  
        }  
        else  
        {  
            tem=m/wh[i].f;  
            res+=wh[i].w*tem;  
            break;   
        }  
    }    
    printf("%.3lf\n",res);     
}  


int main()
{
  double m;
  int n;
  while(scanf("%lf%d",&m,&n) && m!=-1&&n!=-1)
  {
    int i;
    for(i=0;i<n;i++)
      scanf("%lf%lf",&s[i].w,&s[i].f);
    qsort(s,n,sizeof(s[0]),comp);
    printf("\n");
    mxpea(s,n,m);                             
  }
  system("pause");
  return 0;    
}